score = eval(input('请输入您的成绩:'))
if score < 0 or score > 100 :
    print("成绩无效")
# elif 0 >= score and score < 60 :
#     print('E')
# elif score >= 60 and score < 70:
#     print('D')
# elif score >= 70 and score < 80:
#     print('C')
# elif score >= 80 and score < 90:
#     print('B')
# else:
#     print('A')
elif 0<=score<60:
    print('E')
elif 60<=score<70:
    print('D')
elif 70<=score<80:
    print('C')
elif 80<=score<90:
    print('B')
else:
    print('A')